1. Field of the Invention
The present invention relates to a wave gear drive, and in particular to a lubricant supplying mechanism for a wave gear drive that can supply lubricants appropriately to a wave bearing portion and meshing portions between internal and external gears, respectively.
2. Related Art Description
A typical wave gear drive is constituted by a cylindrical rigid internal gear having inner teeth, a cylindrical flexible external gear having external teeth meshable with the inner teeth, and an elliptical wave generator which flexes the external gear elliptically to mesh the external teeth partially with the internal teeth of the internal gear and rotates the meshed portions of teeth circumferentially. The wave generator comprises a rigid cam plate having an elliptical profile and a wave bearing fixed between the circumferential outer surface of the cam plate and the circumferential inner surface of the external gear.
When the rigid cam plate is rotated, relative rotation is generated between the internal and external gear due to the difference in tooth number between the internal teeth and the external teeth. Generally, the tooth number of the internal teeth is larger than that of the external teeth by two, and when high speed rotation is input to the wave generator from a motor or the like, an output rotation whose speed is greatly reduced can be obtained from the flexible external gear by fixing the rigid internal gear so as not to rotate.
In a conventional wave gear drive, inside and outside portions of the flexible external gear are in communication with each other, and therefore lubricant can be circulated freely between the inside and outside portions thereof. Circulation of the lubricant may prevent portions to be lubricated from being supplied with sufficient lubricant.
Further, in a conventional wave gear drive, a common lubricant is supplied to meshing portions of the internal and external gears and to the wave bearings. It is, however, preferable that a lubricant to the teeth of the internal and external gears which are located outside the flexible external gear is of a type having high viscosity because it has high film strength. While, a lubricant to the wave bearing located inside the flexible external gear is preferably of low viscosity because agitating resistance thereof is low.
In consideration of the above point, it is preferable to supply different lubricants to the teeth portion and the wave bearing. However, the inside and outside portions of the flexible external gear are in communication with each other as mentioned above, the lubricants of different type may mix with each other during operation of the wave gear drive. This may cause to degrade the properties of both lubricants, and in the end, effects or advantages obtained by using different lubricants cannot be expected.